Change value of sun light emission strength from Python console or script
Yes the tooltip can be a little misleading, look for the node_tree property on the lamp data object.

With the lamp as context object 

&gt;&gt; C.object
bpy.data.objects['Lamp']

&gt;&gt;&gt; C.object.data.node_tree.nodes['Emission'].inputs['Strength'].default_value = 2


# or via bpy.data (D)

&gt;&gt;&gt; D.objects['Lamp'] == C.object
True

&gt;&gt;&gt; D.objects['Lamp'].data
bpy.data.lamps['Lamp']

&gt;&gt;&gt; lamp = D.lamps['Lamp']

&gt;&gt;&gt; lamp.node_tree.nodes['Emission'].inputs['Strength'].default_value = 3